The present invention relates to a semiconductor acceleration sensor and a method of producing the sensor, and particularly to a semiconductor acceleration sensor comprising a pedestal on which a semiconductor acceleration sensor chip is mounted and a stopper for stopping unnecessary movement of a weight, both of which are integrally formed, and a method of producing the sensor.
FIG. 5 is a sectional side view taken along the center line of a conventional semiconductor acceleration sensor in the lengthwise direction thereof, and FIG. 6 is a plan view of the same. In the drawings, a sensor chip 1 provided with a weight 9 for detecting acceleration is cantilevered from a pedestal 11 which is fixed to a base 5. The base 5 is mounted on a package 4.
As shown in FIGS. 7 and 8, an etched portion 3 is formed in the sensor chip 1 for the purpose of detecting acceleration as a distortion of the chip, and the rear side of the etched portion 3 is provided with a piezoresistance portion 2 which outputs acceleration as a change in resistance. Wiring from the piezoresistance portion 2 is connected to each internal lead 6 through a metal fine wire 12 and to an external circuit (not shown) through external leads 8 which continue from each internal lead 6. Each of the internal leads 6 is insulated from the base 5 by an insulating material such as glass 7. Each of the members such as the base 5, the sensor chip 1 and so on is covered with a cap 10 hermetically sealing the package.
The conventional semiconductor acceleration sensor configured as described above is formed by mounting the acceleration sensor chip 1 on the pedestal 11 by using an adhesive material (not shown) such as a gold-silicon alloy or the like and then mounting the pedestal 11 on the base 5 by using the same adhesive material. The internal leads 6 provided on a package 4 are then connected to an electrode (not shown) for extracting as output distortion in the sensor chip 1 using the metal fine wires 12. The weight is then mounted at an end of the sensor chip 1 by using an adhesive material (not shown), and the cap 10 is then welded to a flange portion 4a provided on the outer periphery of the base 5 of the package 4. The thus-assembled semiconductor acceleration sensor has the structure shown in FIG. 5 in which the metal fine wires 12 are provided on the upper surface of the weight 9 at a distance from the cap 10 so that they do not contact the cap 10.
In the above-described semiconductor acceleration sensor, when acceleration of a degree which is higher than the breaking strength of the residual portion of the etched portion 3 is applied to the sensor chip 1, the sensor chip 1 is broken in some cases. Namely, the thickness of the residual portion of the etched portion 3 of the sensor chip 1 is determined by the measurement range of acceleration in balance with the position and weight of the weight so that the sensor chip is not broken during use within that range. For example, when gravitational acceleration of 1 G is applied to the end of the sensor chip 1, bending of about 1 .mu.m is produced, with allowance of about 400 .mu.m. However, the conventional sensor has the problem that, when acceleration or impact outside the measurement range is applied to the semiconductor acceleration sensor by falling or the like during conveyance, the etched portion of the sensor chip 1 is broken due to the cantilever structure.
The conventional sensor also has the problem that, since the sensor chip 1, the pedestal 11 and the base 5 are bonded to each other using an adhesive material because extremely small flexure is measured, the working accuracy deteriorates, and thus the measurement accuracy of the acceleration sensor is adversely effected.